The invention relates to a method for measuring the growth of leaf disks and to an apparatus suited therefor.
Plant growth is an important cultivation characteristic and is of equally great interest for the analysis of metabolic processes and the influence of active substances on growth.
The use of entire plants results in large space requirements. Moreover, only certain growth habits (notably rosette plants; Walter et al. 2007) are suited for measuring entire leaves. As the coverage of the plant grows with increasing age, such methods are limited to the very early plant stages.
As an alternative to entire plants, the prior art also uses punched-out leaf disks. Punched-out leaf disks will continue grow for days in suitable nutrient solutions (Walter 2000). This allows measurement of the growth of numerous plants in a space-saving manner, with high throughput. Moreover, leaf disks allow for easy application of active substances.
Conventional methods for optically measuring leaf growth generally use entire plants. The optical determination of the surface of individual plants is carried out either in two dimensions, which is to say by measuring the projected leaf area (Granier et al. 2006; Walter et al. 2007) or three dimensions, which is to say with a surface model obtained using a laser scanner or stereo camera (Kaminuma et al. 2004). In addition, commercially available systems exist for measuring the area of leaf disks located on a fixed subsurface (for example, LemnaTec GmbH). The latter are used, for example, to quantify feeding damage by herbivores or damage caused by fungal diseases.
Leaf disks for growth experiments must float freely in solution because a solid base significantly impairs the growth. The subsiding liquid level over the course of the experiment decreases the projected area, which is superimposed with the actual increase in area. Conventional optical 2D measurement methods are therefore not able to determine the actual growth rate. For leaf disks that have high growth rates, the subsiding liquid level only causes the actual growth rates to be underestimated. For leaf disks with lower growth rates (in the range of the seemingly negative growth measured as a result of the subsidence), no meaningful measurement is possible at all. Because a large number of plants have pronounced diurnal growth cycles, the measurement of the actual growth rates is immensely important.
Inclined or curved leaf disks (the latter occurs, for example, under the action of phytohormones) lead to a smaller projected area. Growth can also not be measured using non-stereo methods.